Code:
smtplib.SMTPAuthenticationError: (534, b'5.7.9 Application-specific password required. Learn more at\n5.7.9 https://support.google.com/mail/?p=InvalidSecondFactor d14-20020aa7ce0e000000b0051bed21a635sm374014edv.74 - gsmtp')
2 factor auth is failing.
https://support.google.com/accounts/...form%3DDesktop
I don't believe this is supported by Calibre.